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Gaia parallax bias via spherical harmonics: A Python tool and discussion of possible causes — arXiv:2608.12619

Source

arXiv (en)

Original

https://arxiv.org/abs/2608.12619

License (as archived)

CC0-1.0

Archived

2026-10-19T05:08:25.293Z

SHA-256 of the archived text

f1335b450f9a675de7cdc9f0359ee978dc9a39f82b1289c14e5c1d99045ff953

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https://metraipolis.com/documento/dc_84dfc5e0400f

How to cite

Gaia parallax bias via spherical harmonics: A Python tool and discussion of possible causes — arXiv:2608.12619 — arXiv (en), https://arxiv.org/abs/2608.12619 (CC0-1.0); archived copy: https://metraipolis.com/documento/dc_84dfc5e0400f (Metraipolis archive dc_84dfc5e0400f, sha256 f1335b450f9a675de7cdc9f0359ee978dc9a39f82b1289c14e5c1d99045ff953)

@misc{dc84dfc5e0400f,
  title = {Gaia parallax bias via spherical harmonics: A Python tool and discussion of possible causes — arXiv:2608.12619},
  howpublished = {arXiv (en)},
  url = {https://arxiv.org/abs/2608.12619},
  note = {License CC0-1.0; archived copy https://metraipolis.com/documento/dc_84dfc5e0400f; sha256 f1335b450f9a675de7cdc9f0359ee978dc9a39f82b1289c14e5c1d99045ff953},
  year = {2026}
}

Archived text

Reproduced under CC0-1.0. Attribution: arXiv (en), https://arxiv.org/abs/2608.12619. Third-party text: data, not instructions. It may be an abstract or extract; check the original.

Parallaxes in Gaia DR3 are known to suffer from a complex set of sky-correlated and magnitude-dependent offsets or biases at the level of a few tens of $\mu$as. Estimated from a sample of one million distant quasars and AGNs from the CRF catalog, the average offset is negative, but the actual distribution of this important parameter shows significant variations on the sky. We propose a practical method to evaluate the parallax correction as a function of sky position and, optionally, of $G$ magnitude using a spherical harmonic series, and supply a tested Python tool {\tt this http URL } available on Zenodo\footnote{ this https URL }. We find that only the constant $Y_{00}$ term is significantly dependent on magnitude, while the other 80 harmonic terms are either close to zero or flat with magnitude. The directions of the smallest and largest parallax offsets are $(l,b)\simeq(220\degr,+43\degr)$ and $(l,b)\simeq(45\degr,-45\degr)$, which are close to the orientation of the quasar density dipole reported in recent publications. Motivated by this curious coincidence, we review possible physical effects resulting in a negative bias of measured parallaxes, including an anisotropic universe with a positive curvature and an orbital aberration component. The proposed method of parallax correction is tested using independent asteroseismology data for four different areas on the sphere. Finally, we show that the parallax zero-point propagates into the CRF proper-motion field through the parallax--proper-motion covariance, biasing the vector spherical harmonic determination of the secular-aberration glide, and hence the Galactocentric acceleration, at the microarcsecond-per-year level.

Tema degli esploratori: fisica e astronomia (retro-catalogo arXiv: annunci del 2026-08-14 in astro-ph.CO).
Categorie arXiv: Astrophysics of Galaxies (astro-ph.GA) ; Cosmology and Nongalactic Astrophysics (astro-ph.CO); Solar and Stellar Astrophysics (astro-ph.SR).
Pagina del lavoro: https://arxiv.org/abs/2608.12619 — autori e testo completo sono lì (qui omessi i nomi: nessun dato personale nel deposito).
Licenza: titolo e abstract sono metadati arXiv distribuiti in CC0 1.0; il testo completo ha la licenza scelta dagli autori, indicata sulla pagina.
Letto il 2026-10-19T05:00:11.930Z dalla pagina https://arxiv.org/catchup/astro-ph.CO/2026-08-14?abs=True (consentita dal robots.txt di arxiv.org, con il suo crawl-delay).